3-channel double relaxation oscillation SQUID magnetometer system with simple readout electronics

109

This review paper illustrates the different SQUID based systems used for biomagnetic imaging. The review is divided into nine sections. The first three sections are introductory: section 1 is a short overview of the topic; section 2 summarizes how the biomagnetic fields are generated and what are the basic mathematical models for the field sources; section 3 illustrates the principles of operation of the SQUID device. Sections 4-8 are specifically devoted to the description of the different systems used for biomagnetic measurements: section 4 discusses the different types of detection coils; section 5 illustrates the SQUID sensors specifically designed for biomagnetic applications together with the necessary driving electronics, with special emphasis on high-temperature superconductivity (HTS) SQUIDs, since HTS devices are still in a developing stage; section 6 illustrates the different noise reduction techniques; section 7 describes the different multichannel sensors presently operating; and, finally, section 8 gives a hint of what kind of physiological and/or clinical information may be gathered by the biomagnetic technique. Section 9 suggests some future trends for the biomagnetic technique.

Section: Drosmentioning

confidence: 99%

Section: Drosmentioning

confidence: 99%

SQUID systems for biomagnetic imaging

Pizzella

Penna

Gratta

et al. 2001

109

“…The size of each Josephson junction in the signal SQUID is 4 × 4 µm 2 . In particular, in order to reduce the number of wires between the DROS and the readout electronics and also to reduce the possibility of flux trapping by the reference SQUID, we adopted a reference junction instead of the reference SQUID [8]. The size of the reference junction is 5×5 µm 2 , so that its critical current is 78% of the maximum critical current of the signal SQUID.…”

Section: Design and Layout Of The Devicementioning

confidence: 99%

An integrated planar gradiometer based on a double relaxation oscillation SQUID

Lee

Kwon

Kim

et al. 1996

The design and performance of an integrated planar gradiometer based on a double relaxation oscillation SQUID (DROS) are presented. The DROS was made from hysteretic Nb/AlO x /Nb junctions and the devices were fabricated by a simple four-level process. The signal SQUID loop is a gradiometric type with two square holes connected in parallel and a reference junction is used instead of the reference SQUID. The high flux-to-voltage transfer coefficient of typically 3 mV −1 0 enabled direct readout by a simple electronics with a modest voltage noise. The pickup coil integrated on the same wafer as the SQUID consists of two planar 10 × 10 mm 2 coils connected in series and has a baseline of 30 mm. The overall size of the device is 10 × 40 mm 2 . The field gradient noise is 2.6 fT cm −1 Hz −1/2 in the white region and 4.4 fT cm −1 Hz −1/2 at 1 Hz.

“…In order to reduce the preamplifier noise, a transformer to match the low impedance of the SQUID to the high impedance of the preamplifier is used in the so-called flux modulation scheme [2]. Some other 4 Author to whom any correspondence should be addressed. approaches are described in detail in [1], e.g., the two-stage configuration [3], the double relaxation oscillation SQUID [4], and further readout schemes.…”

Section: Introductionmentioning

confidence: 99%

“…Some other 4 Author to whom any correspondence should be addressed. approaches are described in detail in [1], e.g., the two-stage configuration [3], the double relaxation oscillation SQUID [4], and further readout schemes.…”

Section: Introductionmentioning

confidence: 99%

A voltage biased superconducting quantum interference device bootstrap circuit

Xie

Zhang

Wang

et al. 2010

We present a dc superconducting quantum interference device (SQUID) readout circuit operating in the voltage bias mode and called a SQUID bootstrap circuit (SBC). The SBC is an alternative implementation of two existing methods for suppression of room-temperature amplifier noise: additional voltage feedback and current feedback. Two circuit branches are connected in parallel. In the dc SQUID branch, an inductively coupled coil connected in series provides the bias current feedback for enhancing the flux-to-current coefficient. The circuit branch parallel to the dc SQUID branch contains an inductively coupled voltage feedback coil with a shunt resistor in series for suppressing the preamplifier noise current by increasing the dynamic resistance. We show that the SBC effectively reduces the preamplifier noise to below the SQUID intrinsic noise. For a helium-cooled planar SQUID magnetometer with a SQUID inductance of 350 pH, a flux noise of about 3 μ 0 Hz −1/2 and a magnetic field resolution of less than 3 fT Hz −1/2 were obtained. The SBC leads to a convenient direct readout electronics for a dc SQUID with a wider adjustment tolerance than other feedback schemes.